In a conventional technique for forming semiconductor devices by etching, a photoresist etching mask is formed on a surface of the body or layer to be etched. The pattern of the mask is chosen to protect preselcted areas from attack by the etchant species. Upon application of etchant to the surface, whether by wet chemical etching techniques, plasma etching techniques, etc., the etchant attacks and removes exposed portions of the surface, ideally leaving well-defined unetched area(s) coinciding with the area(s) covered by the mask.
Unfortunatly, resolution between etched and unetched areas is difficult to achieve at best, and is adversely affected by various etching parameters. Problems with resolution can be very difficult to solve and indeed can be a limiting factor in achieving the increasingly small, fine structures required by the microelectronics industry. In particular, photoresist adheres poorly to the silicon and polysilicon which is widely used in the microelectronics industry, with resulting poor etch resolution and the attendant problems with dimensional control, and wafer yields, device performance, etc.
One solution to the problem of photoresist-to-polysilicon adhesion is to use a different mask material. Probably the most widely used and best non-photoresist masking technique (in terms of adhesion) uses an oxide mask which is deposited or thermally grown on the polysilicon. One suitable procedure is to place the polysilicon body (typically a polysilicon coating on a partially processed semiconductor wafer) in a furnace at about 1000.degree. C. in dry oxygen for about 11/2 hours to thermally grow a 900 Angstroms thickness layer of silicon oxide out of the polysilicon. The relatively thick oxide layer is then formed to a mask for the polysilicon. The oxide provides a generally excellent mask for etching the polysilicon in wet chemical etchants such as a nitric acid-HF-acetic acid system.
It is believed oxide masks have not been used for plasma etching. Regardless of the etching technique used, the oxide masking procedure involves the combination of thermal growth, mask formation and mask removal and is thus time-consuming and relatively costly.
A different approach is to enhance the adhesion between polysilicon and photoresist by applying an intervening layer of hexamethyldisilazane (HMDS). This is a relatively simple operation, but the adhesion is still not great, as indicated by the characterization of sample Nos. 2A-2C in the Table below.
RF plasma techniques have been used to facilitate the etching of microelecronics materials. For example, U.S. Pat. No. 3,951,709 issued Apr. 20, 1976 to Jacob teaches the use of a plasma of oxygen and a chlorinated compound (halogen-containing compound) to etch a metallized material without degradation of the photoresist etching mask. U.S. Pat. No. 3,920,483 issued Nov. 18, 1975 to Johnson et al. relates to treating a preformed photoresist mask with plasma to prevent flowing of the photoresist material during subsequent ion implantation. U.S. Pat. No. 3,816,196 issued June 11, 1974 to LaCombe teaches a method of using plasma to passivate an organic photoresist to the effects of a subsequent plasma etch. As is evident, these patents relate to treating or otherwise affecting a photoresist mask after its formation on the material to be etched and do not relate to enhancing the adhesion between the photoresist and the masked body.
As may be thus appreciated, it is desirable to have a quick, simple technique for enhancing the adhesion of photoresist material to polysilicon.